/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode() : val(0), next(nullptr) {}
 *     ListNode(int x) : val(x), next(nullptr) {}
 *     ListNode(int x, ListNode *next) : val(x), next(next) {}
 * };
 */
 class Solution {
  public:
    ListNode* deleteDuplicates(ListNode* head) {
      for (auto cur = head; cur; ) {
        if (cur->next && cur->next->val == cur->val) {
          cur->next = cur->next->next;
        } else {
          cur = cur->next;
        }
      }
      return head;
    }
  };